Millions of people worldwide are afflicted with conditions of the bladder including hemorrhagic cystitis, interstitial cystitis/painful bladder syndrome (IC/PBS), and cancer. Hemorrhagic cystitis is characterized by recurrent hematuria, urinary urgency, and supra pubic pain. IC/PBS is a chronic and painful inflammatory condition affecting about 700,000 to 1 million people in the U.S. alone, of which, ninety percent are women. Urinary bladder cancer is the fourth most frequently diagnosed cancer in men and the ninth most frequently diagnosed cancer in women. There are approximately 56,000 new cases of bladder cancer diagnosed each year. 12,000 deaths each year are attributed to bladder cancer.
Intravesical therapies have been a mainstay in bladder treatments for many years (Parkin, et al., Urol., 49, 105-107 (1997)). Liposomes are biodegradable, non-toxic, unilamellar or multilamellar vesicles formed from naturally occurring or synthetic phospholipids. Liposomes have an ability to entrap and retain a wide range of therapeutic agents, either in their aqueous (hydrophilic agents) or their lipid (hydrophobic) phases (Senior, Crit. Rev. Ther. Drug Carrier Sys., 3, 123-193 (1987); Lichtenberg, Methods Biochem. Anal., 33, 337-362 (1988); Gregoriadis, Subcell. Biochem., 14, 363-378 (1989); Reimer, et al., Dermatol., 195:93 (1997)). Liposomes have been used in clinical practice for treatment of metabolic disorders (Gregoridis, et al., Prog. Clin. Biol. Res., 95, 681-701 (1982), infectious diseases (Richardson, J. Clin. Pharmacol., 29, 873-884 (1983), systemic fungal infections (Grant, et al., Biochem. Biophys. Acta, 984, 11-20 (1989) and to reduce the adverse systemic effects of chemotherapeutic drugs (Owen, et al., Anticancer Drugs, 3, 101-107 (1992); Gabizon, et al., Acta Oncol., 33, 779-786 (1994)). U.S. Pat. Nos. 7,063,860 and 8,110,217, both by Chancellor, et al., disclose liposomal delivery of capsaicin or botulinum toxin, respectively, to urothelial cells for treatment of bladder dysfunction. Twelve liposomal-therapeutic agent formulations have been approved by the U.S. Federal Drug Administration and an additional twenty-two were in clinical trials (Chang, et al., Scientific Rep., 1, 195 (2012)).
Liposomes containing therapeutic agents are delivered to a target cell primarily by whole-liposome endocytosis or phagocytosis and by direct fusion of a liposome membrane with a target cell membrane. Current liposomal therapies primarily utilize the endocytotic pathway due to the small (sub-micron), thermodynamically stable spherical structure of the constituent liposome particles liposomal particles.
Current liposomal formulations have several disadvantages, particularly delivery of hydrophobic agents, due to the small, stable structure of the liposomes. Small liposomes experience great expansive stress and high membrane bending energies due to their small radii of curvature. This forces the small liposomes to be in an entropically unfavorable, yet thermodynamically stable, spherical conformation. Small liposomes have a limited potential to react with membranes of target cells. Current liposomal therapies rely primarily on endocytosis, as opposed to direct membrane fusion, for delivery, which has implications for delivery of hydrophobic agents.
Hydrophobic compounds are often rapidly (within minutes) depleted from the lipid bilayers of liposomes by exchange mechanisms, leading to their equilibration amongst all other lipidic structures within systemic circulation (lipoproteins, erythrocyte membranes, etc.) (Fatouros and Antimisiaris, J. Drug Target, 9, 61-74 (2001); Fahr and Seelig, Crit. Rev. Ther. Drug Carrier Syst., 18, 141-172 (2001); Ardhammar et al., J. Biomol. Struct. Dyn., 17, 33-40 (1999)). Rapid clearing of liposomes is not completely absolved by local delivery of liposomal formulations, as lipidic structures also exist in local environments. Uptake by endocytosis is comparatively slow compared to direct fusion with the target cell membrane. Therefore, current liposomal formulations can lose more hydrophobic agent to the environment while undergoing endocytosis, than if the liposomal formulation utilized a more direct pathway. Thus, there is a need for improved methods of hydrophobic therapeutic agent delivery by liposomal formulations.
It is an objective of the invention to provide metastable liposomes which provide improved delivery of hydrophobic therapeutic agents, for example, by direct application to tissue or a tissue lumen such as the bladder for treatment of hemorrhagic cystitis, IC/PBS, cancer and other disorders.